The present invention relates to an optical signal sampling apparatus suitable for high-speed gating of optical signals to be measured. More particularly, the present invention relates to a novel optical signal sampling apparatus that is suitable for application to a high-speed light waveform measuring system and which is capable of efficient gating (sampling) of optical signals, with the added advantage that the timing of sampling can be controlled electrically in an easy way.
Devices conventionally used to sample optical signals include a mechanical chopper using a rotating plate with a slit, an optical Kerr shutter having a Kerr cell which is filled with CS.sub.2 or other organic solvent and held between a pair of orthogonally crossed polarizing elements, and a liquid-crystal shutter.
These conventional apparatus, however, have their own problems. A mechanical chopper is limited in its operating speed and involves difficulty in control. An optical Kerr shutter has the need to apply a high (.perspectiveto. 1 kV) voltage to produce double refraction in the cell medium and this presents difficulty in handling, besides the need to employ a complicated power source. Furthermore, because of the use of polarized light waves, a pair of orthogonally crossed polarizing elements must be employed, resulting in great loss of light intensity. A liquidcrystal shutter also needs a pair of orthogonally crossed polarizing elements and causes substantial light intensity loss. In addition, the ratio of transmittance in transmitting state to that in blocking state is much less than 1,000, which is too small to achieve satisfactory sampling. Another problem with the liquid-crystal shutter has been the difficulty encountered in attempts to improve the sampling rate and gating time.